Communication systems are well known in the art. Generally, such systems comprise communication stations, which transmit and receive communication signals between each other. In a communication system, an equalizer is commonly applied to a received signal to remove signal distortion caused in the channel. Equalization is especially useful in wireless communication systems where communication signals suffer distortion effects due to interfering transmissions in a shared wireless channel.
In its most basic form, equalization is a method for separating a desired signal from interfering signals. In addition to performing equalization, it is also desirable to correct other types of signal distortion that typically result from receiver imperfections. Some examples of signal distortions caused at the receiver include direct current (DC) offset, carrier phase offset and in-phase and quadrature signal imbalances in the case of quadrature amplitude modulation (QAM) schemes.
Methods for adapting a filter to counteract distortions in a received signal by exploiting statistical properties of the received data are generally referred to as blind equalization. Blind equalization is desirable for removing distortion from a received signal because it is more bandwidth efficient than equalization techniques that require a training sequence to be transmitted with the data stream.
Blind equalization using independent component analysis (ICA) in applying well-known ICA signal separation algorithms in a frequency domain has been proposed in the prior art. The prior art applications of ICA for blind equalization are based on correcting distortions resulting from receiver imperfections in the time domain while signal equalization is performed in the frequency domain. The inventors have recognized that one disadvantage of the prior art is that some imperfections, such as DC offset, are a result of coefficient truncation in the equalizer and therefore require a separate DC-offset remover following equalization.
The inventors have developed an ICA-based method for equalization in the time domain that enables equalization and compensation for receiver imperfections to be performed together, thus allowing ICA to correct all sources of signal distortion simultaneously and improving upon the inefficiencies of the prior art.